While the pitcher stands on The Hill (pitcher's mound), he's often said to be Toeing the Slab. His mission: to get those pesky batters out. If the pitcher is left handed, he's a South Paw. While some would think it's an insult to yell "pitcher's got a Rubber Arm," it's actually not because that just means his arm never gets tired.
Pitchers are often said to have a Gun... and I don't mean a firearm. It's just a strong throwing arm. A Hurler who has a Live Arm can throw Smoke (high velocity pitches) until the cows come home! He'll throw the Heater (fastball) right by a batter. But sometimes he might throw some Junk (sinker, forkball, screwball) or Take Something Off The Pitch to keep the batters on their toes. Other times, if the pitcher is ahead in the Count (number of balls and strikes), he might try to Waste a Pitch and throw some High Heat (high fastball) attempting to get the batter to swing at a pitch out of the strike zone.
My favorite of all the pitches is the curveball. It's an Uncle Charlie, a Hook that basically drops out of the strike zone 12-6 (like on the clock)—not the easiest pitch to hit. A good Bender will fool the best of the hitters when the Bottom Drops Out. And then there are those times when his stuff just isn't working and he ends up throwing a big, fat Meat Ball that ends up in the stands for a home run. Meat Balls are bad.
Sometimes pitchers are forced to pitch defensively to keep the guy at the Dish (home plate) honest. Maybe he's leaning in too far and Crowding the Plate... the pitcher might throw some Chin Music (a pitch that buzzes a player's face) to back him off. Or he might Handcuff the batter to make it difficult for him to make a full swing. There might also be a situation when maybe a player has been a little too good at the plate and the guy on the mound if forced to either Pitch Around the Hitter (intentionally throw bad pitches so he has nothing to hit) or he might Drill or Plunk (hit by pitch) that batter to teach him a lesson.
Getting Shelled is bad. It means the pitcher has given up a lot of runs. You don't want this to happen. His main purpose is to get guys out and the best way—a Punch Out (no, not fisticuffs, it's a strikeout.) And hopefully he can Ring Up three guys in a row by making them Whiff (swing and miss) and Strike Out the Side (strikeout all three batters in one inning.)
See? Lots of lingo to learn and there's still so much more to go. Try watching some spring training baseball games and see if you can put your new found vocabulary to good use!